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Attitude Control System

VIEWS: 18 PAGES: 37

  • pg 1
									                  NMP EO-1
                  NMP /EO-1                               DELTA PRE-SHIP REVIEW




                               Section 19
                          Attitude Control System



                                                                 . . . Paul Sanneman
Day 1: 08/09/00
                                                                                    Inc.
                                 EO-1 ACS Lead Systems Engineer, Swales Aerospace, 19 - 1
                  NMP EO-1
                  NMP /EO-1                                         DELTA PRE-SHIP REVIEW


                                             Contents
                      Attitude Control Subsystem Block Diagram
                      Changes since March 2000 Red Team Review
                      Thermal/Vacuum II Evaluation
                      Open Problem Reports
                      Special Topics
                       –   IRU Removal and Reinstallation
                       –   On-orbit Testing of Safe Hold Mode
                       –   Autonomous Star Tracker Issues (including IMAGE AST issue)




Day 1: 08/09/00                                                                         19 - 2
                  NMP EO-1
                  NMP /EO-1                                              DELTA PRE-SHIP REVIEW


                         ACS Architecture Block Diagram
                     Revised: 11 SEP 98
                                                                                         GPS Receiver,
                                                                                         Pre-amp &
                                                 H/K RSN                                 Antennas
                     Autonomous


                                          1773
                                                 MV CPU                                  Three Axis
                     Star Tracker                                                        Magnetometer
                                                  ACS FSW
                                                                                         Coarse Sun
          Inertial                                                                       Sensors (4)
                                                 ACE RSN
          Reference                                                                         Reaction
                                                   SHM
          Unit                                                                              Wheels
                                                                                            & MDE (3)

                                                         ACE BACKPLANE
                                   ECU
                                                 ACE                                      Magnetic
                  SAD                            I/O                                      Torquer
                                                                                          Bars (3)

                                                 PROP                    Thrusters (4)
                        Pulsed Plasma             I/O
                        Thruster

                                                 ACE
                                                 LVPC
Day 1: 08/09/00                                                                                          19 - 3
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                  NMP /EO-1   DELTA PRE-SHIP REVIEW

“As Run”
Verification
Matrix




Day 1: 08/09/00                                 19 - 4
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Projected
Power On
Time




Day 1: 08/09/00                                 19 - 5
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                  NMP /EO-1                                              DELTA PRE-SHIP REVIEW


                       Changes Since Red Team Review
                      ACS Components
                       –   AST & ACDS DC/DC Converter lid stiffeners (see Special Topic)
                       –   Removed IRU to prevent helium exposure (see Special Topic)
                      ACE Software
                       –   ACE RSN S/W update to Version 3.11 on 8-JUN-00
                            – PTR0927: Generic Code modified to have IRAM2 checksum
                              protection on [had been missed since ACE is the only RSN with the
                              extended RAM capability]
                            – PTR0939: Prevent ACE 25 Hz Event Messages and use telemetry
                              error counters instead
                       –   Code changes tested on 8-JUN-00; 416+ failure free hours
                      M5 ACS Software
                       –   Minor parameter changes via M5 Table loads to RAM
                       –   Related to improving operation issues - no S/C safety issues

Day 1: 08/09/00                                                                                   19 - 6
                  NMP EO-1
                  NMP /EO-1                                              DELTA PRE-SHIP REVIEW

                        Summary of Open Items from
                        March Red Team Review (1 of 2)
                       Verification Matrix, no update necessary (page 18-14)
                       Updated operating hours included on Slide 7-5 (page 18-15)
                       PR 674-20-41 AST number of stars issue (page 18-19)
                         –   Confirmed this is a star field simulator issue (see Slide 19-9)
                       GPS tensor warm start ground procedures (page 18-20)
                         –   Fully tested and available in MOC ASIST
                       No updates to SHM from final CPT (page 18-34)
                       Updates to remaining work
                         –   AST/IRU alignment…detailed in Slide 19-10
                       Conclusion of AST DC/DC Converter concern (18-40)
                         –   See Special Topic on AST DC/DC Converter

Day 1: 08/09/00                                                                                19 - 7
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                  NMP /EO-1                                             DELTA PRE-SHIP REVIEW

                         Summary of Open Items from
                         March Red Team Review (2 of 2)
                       Updated summary of IRU PDV history (page 18-49)
                         –   Details in Special Topic. No outstanding performance issues.
                       SIRU return to spacecraft (page 18-57)
                         –   Details in Special Topic. Reintegration successful. Degradation
                             reversed.
                       Open actions from ACS Phasing Review (page 18-63)
                         –   CPT phasing tests following final MV S/W load -completed
                         –   CSS phasing following final solar array attachment -completed
                         –   Final magnetic phasing completed on 28-JUL-00 - no issues




Day 1: 08/09/00                                                                                19 - 8
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                  NMP /EO-1                                              DELTA PRE-SHIP REVIEW


                        Thermal Vacuum II Test Results
                      Attitude Control Subsystem performance validated as part
                       of CPT segments and via other special tests
                        –   All CPT associated tests run at hot and cold plateaus
                        –   RWA Overspeed protection verified at hot and cold plateaus
                        –   AST Thermal Electric Cooler operation modes verified
                        –   AST TEC default state and Effective Focal Length
                            changed/restored during T/V II as demonstration of planned
                            on-orbit maintenance procedures
                        –   IRU internal heater control of gyro platform validated




Day 1: 08/09/00                                                                            19 - 9
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                  NMP /EO-1                                            DELTA PRE-SHIP REVIEW


                             Reaction Wheel Assemblies
                      RWA performance has been verified in both air and
                       vacuum
                        –   Control torques issued by override and closed-loop software
                      Overall run-up and coast down trends have been verified
                       with vendor and are summarized on next page
                      T/V II testing of overspeed protection provided below with
                       wheel speeds in RPM




Day 1: 08/09/00                                                                           19 - 10
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                  NMP /EO-1                            DELTA PRE-SHIP REVIEW


             RWA Run-up / Coast Down Trend Table




                           Trending data is consistent over time.
              Estimated drag torque very consistent and near 50% of spec level
Day 1: 08/09/00                                                            19 - 11
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                                      Critical PR Status
                      PR-468-20-4 IRU Parametric Drive Voltage
                        –   See Special Topic
                      PR-674-20-41 AST Number of Stars = 18
                        –   Issue and problem report have been closed
                        –   Similar operation noted on the MAP ASTs during Thermal/Vac
                            testing at the component level
                        –   Investigation of MAP occurrence with AST-GSE confirmed this is a
                            Star Field Stimulator GSE issue
                        –   Contamination on lens of GSE can cause double reflection that
                            causes a „match‟ with a very dim star in the AST internal star
                            catalog




Day 1: 08/09/00                                                                                19 - 12
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                  NMP /EO-1                                            DELTA PRE-SHIP REVIEW


                                  ACS Flight Readiness
                      ACS components and hardware are ready
                      ACS and ACE software are ready
                      ACE Safehold Mode is ready
                      Ops preparations/training are ready
                      Remaining Work
                        –   No outstanding problems or issues
                        –   AST/IRU alignment measurements at launch site
                      Red Book Item: IRU sensitivity to helium exposure
                        –   Under control via upgraded purge system on S/C and at launch site


                                 Attitude Control Subsystem is READY


Day 1: 08/09/00                                                                                 19 - 13
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                                Special Topic:
                              Star Tracker Issues




                                                             . . . Wayne Roher
                                                        Litton Advanced Systems
Day 1: 08/09/00                                                            19 - 14
                  NMP EO-1
                  NMP /EO-1                                                       DELTA PRE-SHIP REVIEW

                       AST Interpoint DC/DC Converters
                                 Failure Mode
                      MAP experienced failure with ± 15V DC/DC converter
                        –   MAP2 - Open failure during ATP at ambient after Thermal/Vacuum
                             – DPA indicate inadequate stress relief on internal bond wire, insufficient
                               solder, and solid adhesive attachment to lid caused bond wire to pull away
                               from pad in vacuum.
                      EO-1 AST X-ray investigation
                             – The two DC/DC converters on the EO-1 AST were X-rayed and found to
                               have met the criteria determined by Code 562 as having sufficient relief
                               distance from the transformer.
                      Code 562 speculated that an additional failure mode exists
                             –     “Oil canning” of converter package could cause adhesive on bottom of
                                 transformer to release. Transformer would move upward with package lid,
                                 causing transformer bond wire to pull away even if adequate stress relief
                                 existed for normal operation in a vacuum.




Day 1: 08/09/00                                                                                              19 - 15
                  NMP EO-1
                  NMP /EO-1                                               DELTA PRE-SHIP REVIEW


                       AST Interpoint DC/DC Converters
                                   Rework
                      Lockheed Martin Palo Alto and Lockheed Martin Mission Success
                       agreed that this failure mode potential justified corrective action.
                      Stiffening the lid to prevent “oil canning” was determined to be the
                       best solution to address all concerns of stress, unattached
                       adhesives, and vibration.
                      Lid stiffener of 20 mil Kovar and minimum 5 mil bond line of epoxy
                       was added to both D/CDC converters. (See Converter Lid
                       Stiffening Special Topic)
                      Both converters tested to deflect less that 1 mil in vacuum




Day 1: 08/09/00                                                                               19 - 16
                  NMP EO-1
                  NMP /EO-1                                             DELTA PRE-SHIP REVIEW

                        AST Interpoint DC/DC Converter
                              Rework Conclusion
                       Retest
                         –   AST workmanship vibration
                         –   AST Functional on Spacecraft
                         –   AST CPT on Spacecraft
                         –   Spacecraft level T/V
                         –   272 hours on time since lid stiffener was added
                       Conclusion
                         –   EO-1 AST has successfully completed all testing post lid
                             stiffening
                         –   EO-1 AST is ready for flight



Day 1: 08/09/00                                                                           19 - 17
                  NMP EO-1
                  NMP /EO-1                                             DELTA PRE-SHIP REVIEW


                       Other Subsystem DC/DC Converter
                          Rework and Re-Qualification
                      All MTRxxD type Interpoint DC/DC Converters were considered as
                       potentially defective due to the failure mode detected on the MAP
                       AST2
                      Two other Subsystems contained Converters that required rework
                        –   GPS PCU (1)
                        –   ACDS box (2); C&DH LVPC and ACE I/O cards




Day 1: 08/09/00                                                                            19 - 18
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                  NMP /EO-1                                            DELTA PRE-SHIP REVIEW


                           GPS PCU DC/DC Converter
                      Rework and Re -Qualification process of GPS PCU
                       –   Removed from Spacecraft
                       –   Added stiffener lids, 40 mil Kovar, 10 mil minimum bond line
                       –   Vacuum test, deflection less than I mil
                       –   One Axis workmanship vibration
                       –   Functional on Spacecraft
                       –   CPT on Spacecraft
                       –   Spacecraft level Thermal Vacuum
                      Conclusion
                       –   No anomalies recorded
                       –   GPS PCU is ready for flight




Day 1: 08/09/00                                                                           19 - 19
                  NMP EO-1
                  NMP /EO-1                                                   DELTA PRE-SHIP REVIEW

                               ACDS DC/DC Converters
                       Rework and Re -Qualification process of ACDS
                         –   Box removed from Spacecraft, C&DH LVPC and ACE I/O boards removed
                         –   Added stiffener lids, 40 mil Kovar, 10 mil minimum bond line
                         –   Vacuum test, deflection less than I mil
                         –   Board level functional tests
                         –   Boards reassembled in ACDS chassis
                         –   Pre-vibe box level Functional Test run
                         –   One Axis workmanship vibration
                         –   Post-vibe box level Functional Test run
                         –   Spacecraft Integration tests
                         –   CPT on Spacecraft
                         –   Spacecraft level Thermal Vacuum
                       Conclusion
                         –   No unexplained anomalies recorded
                         –   ACDS is ready for flight


Day 1: 08/09/00                                                                                  19 - 20
                  NMP EO-1
                  NMP /EO-1                                            DELTA PRE-SHIP REVIEW


                                  Image AST Anomaly

                       The IMAGE AST was unable to acquire between June 9 and
                        August August 3
                       The AST remained in standby mode during this time; power
                        was not recycled
                       On August 3, the AST re-acquired
                         –   1.4 degree angle further from the sun than on June 9
                         –   Dropped out twice during that day, quickly recovered
                         –   Has not dropped out since.




Day 1: 08/09/00                                                                          19 - 21
                  NMP EO-1
                  NMP /EO-1                                               DELTA PRE-SHIP REVIEW


                       Image AST Anomaly Investigation

                     A Failure Review Board (FRB) was held to determine potential
                      causes of the AST acquisition failure.
                     Stray Light is the most probable root cause
                       –   Housekeeping nominal (voltages, temperatures)
                       –   Increased elevated background and reduction in guide star
                           identification were observed during and leading up to the failure to
                           acquire after a loss of track.
                       –   Periodic trending occurred nearest the sun; loss of track and re-
                           acquisition. Symptoms got worse as sun angle decreased.
                       –   Symptoms improved and re-acquisition was attained during eclipse
                           portion of the the orbit.
                       –   No increase in brightness or position error was found.
                       –   All observation are symptomatic of stray light effects.


Day 1: 08/09/00                                                                                   19 - 22
                  NMP EO-1
                  NMP /EO-1                                            DELTA PRE-SHIP REVIEW


                        Image AST Anomaly Investigation

                  Straylight analysis indicates the AST should have been able
                   operate under the current mission attitude.
                    –   The IMAGE AST uses a lightshade (or baffle) designed to keep the
                        sun or Earth out of the boresight (within 12.5 degrees) with no
                        redirected light within 15.1 degrees of the boresight.
                    –   Image minimum bore sight axis to the sun in July at loss of track was
                        22 -42 degrees (AST is 10 degrees off spin axis)
                  Most likely sources of Stray light are:
                    –   Contamination
                    –   Glint from 10 Meter Boom
                    –   Contributions from CCD Mask




Day 1: 08/09/00                                                                                 19 - 23
                  NMP EO-1
                  NMP /EO-1                                           DELTA PRE-SHIP REVIEW


                    Differences Between Image & EO-1

                      Sun Angle
                        –   Image AST approaches within 4 degrees of the Sun
                             – Lost track at 22-42 degrees
                        –   EO-1 AST approaches within 70 degrees of the Sun for
                            nominal nadir pointing operations
                      Baffle differences
                        –   Image
                             – 16 inches
                             – 12.5 degrees of protection from sun
                        –   EO-1
                             – 12 inches
                             – 30 degrees of protection from sun


Day 1: 08/09/00                                                                         19 - 24
                  NMP EO-1
                  NMP /EO-1                                         DELTA PRE-SHIP REVIEW

                              Results of Image AST
                             Anomaly and Investigation
                       Lockheed believes the anomaly occurred due to unknown
                        form of contamination
                       Evidence indicates the AST did not experience a functional
                        failure of the electronics
                       Data indicates the AST is functioning nominally and the
                        data is good
                       Lockheeds preliminary conclusion of the anomaly event
                        and investigation analysis is that this event is not a
                        systemic failure of the ASTs and does not impact the
                        expected reliability of the ASTs built for other missions.
                       Formal conclusion of the FRB is expected late August
                       Lockheed believes EO-1s AST is ready for flight.

Day 1: 08/09/00                                                                       19 - 25
                  NMP EO-1
                  NMP /EO-1                                                    DELTA PRE-SHIP REVIEW

                      What Happens If the AST Fails?
                     AST has been extensively tested on S/C and performance has been
                      nominal. All issues have been aggressively pursued.
                     Demonstrated reliability of product line is less than desirable.
                       –   Error prone manufacturing and test efforts
                       –   Similar AST on DSI failed 15 months into mission
                     Flight dynamics ground based attitude determination could achieve 1
                      to 5 degree pointing accuracy
                       –   Would allow Landsat 7 limited image comparison since we would be within
                           its 15 degree swath width
                       –   Ground attitude estimate developed using TAM and gyro data
                       –   Current flight ACS S/W has capability to use daily uploaded attitude
                           estimate, propagated using gyro data
                       –   Would require some ground software to prepare and uplink daily attitude
                           data; would be developed if AST fails. Sun sensor safehold used until
                           software developed.




Day 1: 08/09/00                                                                                      19 - 26
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                                      Special Topic:
                              IRU Removal and Re-installation




                                                                       . . . Paul Sanneman
                                       EO-1 ACS Lead Systems Engineer, Swales Aerospace, Inc.
Day 1: 08/09/00                                                                          19 - 27
                  NMP EO-1
                  NMP /EO-1                                             DELTA PRE-SHIP REVIEW


                    SIRU Nitrogen Purge - Background

                      Litton Guidance & Control Space Inertial Reference Unit
                      Utilizes three Hemispherical Resonator Gyros (HRGs)
                        –   Quartz crystal hemisphere oscillated at specific amplitude and
                            frequency
                        –   Input angular rate measured by nodal displacement on rim
                      Quartz crystal becomes permeated with Helium
                        –   Increases gaseous damping, requires larger drive voltage -
                            Parametric Drive Voltage (defined as a negative voltage)
                      Not an issue prior to arrival at GSFC Building 7
                      Significant amounts of Helium released in Building 7 by
                       environmental chamber testing processes



Day 1: 08/09/00                                                                              19 - 28
                  NMP EO-1
                  NMP /EO-1                                                    DELTA PRE-SHIP REVIEW


                                Summary of PDV History
                     Activity                                       Date                 PDV *
                     Initial IRU Integration                   15-DEC-1998               -1.04 V
                     EO-1 Arrival at GSFC                       9-JUN-1999               -1.46 V
                     IRU Purge Installation                    10-AUG-1999               -1.81 V
                     End of Initial Building 7 Decline         28-SEP-1999               -2.61 V
                     Prior to Dec 1999 Decline                 1-DEC-1999                -2.59 V
                     Jan 2000 Stabilization                    24-JAN-2000               -2.80 V
                     IRU Removal from S/C                      25-FEB-2000               -2.81 V
                     IRU Reintegration to S/C                  11-MAY-2000               -2.76 V
                     Pre-Thermal/Vac II                        20-JUN-2000               -2.70 V
                     Post-Thermal/Vac II                       25-JUL-2000               -2.66 V

                                   * Gyro A value at turn-on with temperature near 20C


Day 1: 08/09/00                                                                                    19 - 29
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                         Gyro A PDV Slope Estimate




Day 1: 08/09/00                                               19 - 30
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                  NMP /EO-1               DELTA PRE-SHIP REVIEW


                   PDV Trends Since S/C Thermal/Vac




Day 1: 08/09/00                                             19 - 31
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                  NMP /EO-1                                            DELTA PRE-SHIP REVIEW


                              SIRU Return To Spacecraft
                        Re-integration performed 11-MAY-00
                          –   Building 7 air sampling validated low helium concentration
                          –   Building 7 air under constant He monitoring using leak
                              detector
                        Continue to have close coordination with Building 7
                         operations personnel to further minimize exposure
                        Re-integration included new aluminum-wrapped Teflon
                         tube inside spacecraft and stainless steel tube from S/C to
                         tank
                        Gyro Parametric Drive Voltages indicate that both the
                         storage at Swales and the upgraded purge system have
                         reversed the degradation




Day 1: 08/09/00                                                                            19 - 32
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                  NMP /EO-1                                              DELTA PRE-SHIP REVIEW


                                                Outlook
                      Mechanical and launch vehicle I/F engineers have focused
                       activity for IRU protection throughout remaining S/C I&T at
                       GSFC, during transport and launch site processing
                      The increased PDV is NOT a performance issue - just needs to
                       stay within (-5V) capability
                        –   About one volt of margin required for full 10 deg/sec rate capability
                        –   Desire PDV values of 3.5 V (@25C) at time of SC mount on LV
                        –   PDV Voltages on 28-JULY-00: A=-2.66, B=-2.23, C= -2.50 @23C
                      Purge installation on Launch Vehicle (L/V) has been improved to
                       the extent allowable by the L/V vendor/operator
                      Expect Parametric Drive Voltage to remain stable or slight
                       improvement through launch and will slowly recover over the
                       course of the mission - residual risk has been minimized



Day 1: 08/09/00                                                                                     19 - 33
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                                    Special Topic:
                          On-Orbit Testing of Safe Hold Mode




                                                                    . . . Paul Sanneman
                                    EO-1 ACS Lead Systems Engineer, Swales Aerospace, Inc.
Day 1: 08/09/00                                                                       19 - 34
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                  NMP /EO-1                                                DELTA PRE-SHIP REVIEW


                                              RFA 33.33
                       Reviewer:       Ann Merwarth
                       Specific Request:
                         –   Hold a technical peer review with operations experts from
                             outside the project to identify the pros and cons of
                             conducting the safemode test on orbit. Review the results
                             with Center and Program management and ensure that all
                             parties "buy into" the plan for this test. If the Project decides
                             to do this test, we recommend that it be delayed as long as
                             possible.
                       EO-1 Response: Peer review held on 20 APR 2000
                         –   Chaired by Eric Holmes, GSFC Code 571 GNC Systems
                             Engineering
                         –   Board members: Alan Reth, Sam Placanica, Landis Markley




Day 1: 08/09/00                                                                                  19 - 35
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                              Summary of Peer Review
                       Review Agenda:
                        –   Review Team Introductions and Purpose
                        –   Safe Hold Mode Implementation
                        –   Safe Hold Mode Reviews
                        –   Safe Hold Mode Testing during S/C I&T
                        –   On-orbit SHM Test Plans for Two tests
                        –   Benefit/Risk Summary for On-orbit SHM Test
                       Review Conclusion:
                        –   The review panel unanimously agreed with the plan to
                            proceed with the planned on-orbit test of SHM with the
                            following actions to Swales Aerospace




Day 1: 08/09/00                                                                          19 - 36
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                  NMP /EO-1                                                  DELTA PRE-SHIP REVIEW

Peer                         Action 1 (by Sam Placanica):
                               –   Verify that all instruments can survive dwelling on the Sun for at least
Review                             10 minutes.
                                    – ACS, Thermal and Systems investigated and determined that there is
Action                                enough attitude variation following SHM entry to prevent instrument
                                      thermal issues

Items                        Action 2 (by Sam Placanica):
                               –   The duration of the SHM shall be at least 1 complete orbit.
                                    – This is now included in the launch & early orbit mission plan.
                             Action 3 (by review panel):
                               –   Augment test 1 as follows: Have the solar array outside of the 5
                                   degree "indexed" tolerance at the time SHM is initiated, so that SHM's
                                   indexing function via ECU#2 and Pot #2 are demonstrated.
                                    – STOL procedure ACS_SAD_10 developed and tested to perform this
                                      function prior to commanded SHM entry
                             Second SHM test removed from mission plan as there was limited
                              benefit and timing would be obtrusive to instrument
                              activation/checkout

                                         All action items closed. RFA 33.33 closed.
Day 1: 08/09/00                                                                                             19 - 37

								
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